1. Field of the Invention
The present invention relates generally to latching devices, and more particularly to systems for latching hinged doors or panels and the like.
2. Background of the Invention
Various types of latching devices for fastening doors, panels and the like are known.
Door-mounted “slam” latches employ a camming surface on the end of a sliding-bolt element that cooperates with a striker on the door frame to cause a bolt action to secure the door when it is closed against the frame. Such latches are activated to secure the door when the door is merely pushed shut or slammed. However, to open the door, operation of the latch mechanism is required to release the latch. In some slam latches, as the door is being closed, the bolt is urged against a spring force by the action of a camming surface cooperating with the striker to slide into the latch housing. Once the camming surface has passed the door frame inner surface, the spring force then urges the bolt element to engage behind the door frame, or to engage a keeper mounted on the door frame. In order to open the door, the bolt is manually operated, usually through a grip, to withdraw the bolt from engagement with the keeper.
Examples of prior art slam latches are disclosed in U.S. Pat. Nos. 3,841,674, 3,850,464, 5,482,333 and 5,628,634.
The spring force for such latches can be provided through separate spring elements, such as a torsion bar spring (FIGS. 8–9, U.S. Pat. No. 3,841,674), a torsion coil spring (FIGS. 11–13, U.S. Pat. No. 3,841,674), or a compression coil spring (FIG. 13, U.S. Pat. No. 3,841,674). Alternatively, the spring element can be integrally molded with a latch body made from an appropriate plastic or polymeric material (FIGS. 1–7, U.S. Pat. No. 3,841,674; U.S. Pat. No. 5,842,333; FIG. 6A–6E, U.S. Pat. No. 5,628,534).
Slam latches with integrally molded spring elements have a number of advantages over slam latches that use separate metal springs. First, slam latches with integrally molded spring elements tend to be less expensive because fewer parts are required to be made and assembled for each latch. Further, during manufacture metal springs may become embrittled and thus subject to breakage.
On the other hand, prior art latches with integrally molded spring elements may not have the same life expectancy as those that use separate metal springs. Elements formed from polymeric materials that are subjected to cyclic stresses, such as integrally molded spring elements in slam latches, sometimes fail at stress levels far below their yield stress, due to fatigue failure.
Prior slam latches have employed generally planar integrally molded spring elements. Examples include those shown in FIGS. 1–7 of U.S. Pat. No. 3,850,464, and FIGS. 6B–6E of U.S. Pat. No. 5,628,534. A variation is disclosed in U.S. Pat. No. 5,482,333, in which the spring member 5 includes two pairs of integrally hinged generally planar elements, molded from a suitable resin, such as polypropylene, in a relaxed configuration. In each of these designs, when the latch is operated stresses are generated primarily proximate the portion of the latch where the spring extends from the latch body.
There is a need for a simple, inexpensive slam latch having an integrally molded spring element that resists cyclic stresses and fatigue failure.